First, preheat your oven to 350 degrees and grease a 9-inch round cake pan. In a large mixing bowl, combine the cake mix, butter, eggs, milk, and vanilla extract until well-combined. Stir in the sprinkles, making sure they are evenly distributed throughout the batter.
Pour the batter into the prepared cake pan and smooth the top with a spatula. Tap the pan gently on the counter to release any air bubbles.
Place the cake pan in the preheated oven and bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Once the cake is done, remove it from the oven and let it cool completely on a wire rack. While the cake is cooling, you can prepare the frosting.
For this recipe, we'll be using a simple vanilla buttercream frosting, which is made by combining 1 cup of unsalted butter, 4 cups of powdered sugar, 1 tablespoon of vanilla extract, and 2-3 tablespoons of milk.
Beat the ingredients together with an electric mixer until smooth and creamy.